Traumatic brain injury (TBI), particularly mild TBI, has been identified as a signature wound of the wars in Iraq and Afghanistan and concern has been raised about the long-term effects of these injuries on our Veterans. While moderate to severe brain injury has been linked with conditions such as dementia, epilepsy, and movement disorders, the evidence linking mild TBI to neurodegenerative conditions is limited. More recently, studies of football players and boxers have shown long-term effects of concussions and repetitive mild head injuries on cognitive function. This growing awareness of the chronic effects of neurotrauma has led to an urgent need to study the Iraq/Afghanistan Veterans (IAV) who have suffered these types of injuries, including multiple blast related mild TBI. While cognitive dysfunction such as dementia and mild cognitive impairment (MCI) is a significant and growing problem in older adults, it is rare in adults in the age range of IAV (mean age ~36 years), but remains a significant concern due to the high prevalence of mild TBI in the IAV population. To date, observational studies have not been powered to examine the link between mild TBI and rare conditions such as dementia and MCI in younger individuals, and population-based studies using existing data from VA clinical encounters have been limited by concern for the validity of these diagnoses. The National Research Action Plan emphasized the need to understand the association of mild TBI with long-term outcomes such as dementia and MCI so that the Department of Veterans Affairs can plan for the needs of our Iraq/Afghanistan Veterans and provide high quality of care. The long-term goal of the proposed line of research is to address these concerns using a case-control study employing DoD data, VA data and telephone interviews to identify the risk of dementia and MCI among those with deployment-related mild TBI, accounting for lifetime TBI exposure, deployment and non-deployment experiences, and other comorbid conditions such as stroke. However before such a study can be effectively conducted, validation of diagnoses of dementia and MCI in this younger VA population is needed. To address this knowledge gap, we convened an interdisciplinary team with expertise in epidemiology, neuropsychology, neurology, physiatry, and health services research to validate diagnoses of early onset dementia (EOD) and MCI in Iraq/Afghanistan Veterans, and develop algorithms for use in population-based studies of EOD/MCI. We will also describe patient characteristics associated with validated EOD/MCI diagnoses. We hypothesize that among those with diagnoses indicative of EOD/MCI individuals with moderate to severe TBI will be more likely to have validated EOD/MCI diagnoses than similar IAV with mild TBI. This study will develop a cohort that can be used in a larger epidemiological study to examine the impact of deployment related mild TBI on EOD/MCI while controlling for lifetime TBI exposures. Moreover, the process used in this study will allow for development of reliable algorithms for identification of EOD/MCI for population- based research. Findings from these lines of research will inform DoD and VA healthcare systems regarding future resources that will be needed to provide high quality care.